Handheld portable thermally insulated metallic vessel

ABSTRACT

To prevent abrupt deformation of the bottom wall of an inner vessel accompanied by an explosive sound due to expansion of the inner vessel or an insulating medium when heated foods or drinks are placed in the vessel or the vessel is placed in a high temperature environment such as a dryer.  
     A handheld portable thermally insulated metallic vessel  1  comprises a thermally insulated metallic vessel base  2  and a lid  3  to cover said vessel base. The vessel base  2  is fabricated in an integral fashion by joining an inner vessel  4  and an outer vessel  5  to create an airtight space  6  between the outer vessel and the inner vessel, and the airtight space  6  is filled with a gas having a low thermal conductivity and the bottom wall of the inner vessel is formed to have a planar surface.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the priority benefit of Japanese application serial no. 2000-221719, filed on Jul. 24, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a handheld portable thermally insulated metallic vessel having a double wall structure, in particular to a shallow-bottom-type (so called pan-type) portable thermally insulated metallic vessel which can be carried by lifting with both hands.

[0004] 2. Description of the Prior Art

[0005] Generally, in meal providing facilities in schools, factories, hospitals, or the like, a handheld portable thermally insulated metallic vessel having a double walled structure is often used to temporarily store and remain relatively large quantities of food materials at an elevated temperature. This thermally insulated metallic vessel comprises a thermally insulated metallic vessel base and a lid to cover the vessel base. The vessel base has an inner vessel and an outer vessel which are joined in an integral fashion to form a space between the two vessels creating a thermal insulating layer. This thermal insulating layer can be vacuum sealed or filled with air or a gas having a thermal conductivity lower than that of air, depending on the desired thermal insulating capability, cost and the like.

[0006] A vessel having the abovementioned vacuum sealed space generally has an improved thermal insulating capability. However, the vacuum sealing of the space requires a large scale facility and thus the manufacturing cost is high. Moreover, the walls of the inner vessel and the outer vessel have to be thick or a spacer has to be placed between the inner vessel and the outer vessel to prevent deformation since the inner vessel and the outer vessel are constantly under atmospheric pressure.

[0007] A vessel having air in the abovementioned space can be provided at a low cost because it only requires a waterproof structure to prevent invasion of water into the space at the like upon washing so that it can be manufactured without a special process, although it has a poorer thermal insulating capability than a vessel having a vacuum-sealed space. Furthermore, a thermally insulated vessel can be made to have a venthole at the bottom or other place of the outer vessel so as to form an open structure rather than a leakless structure, whereby water or the like invaded into the space can easily escape from the space and the bottom surface of the inner vessel will not be deformed when the air in the space expands.

[0008] Furthermore, a gas filling process is required to manufacture a vessel filled with a gas having a thermal conductivity lower than that of air in the abovementioned space and additionally the space has to be made airtight to prevent leakage of the gas, which increases the manufacturing cost. However, a thermally insulated vessel thus manufactured has an excellent insulating capability as compared to a vessel insulated with air.

[0009] Moreover, a thermally insulated shallow base-type metallic vessel of a size suitable to be held with both hands, such as a vessel used in meal supplying facilities, is manufactured to form a gently concave surface on the bottom wall of the inner vessel, in other words, the space side has a gently convex surface, in order to secure the strrength of the inner vessel.

[0010] Accordingly, in a conventional vessel, the abovementioned concave surface does not provide a stable support for the contents in the vessel above it. For example, cylindrical containers containing drinking water or the like placed inside the vessel easily tipped over, which often caused spilling of drinking water or the like in the containers. Furthermore, when heated foods or drinks were placed in a thermally insulated metallic vessel or the vessel was dried in a dryer at high temperature after washing, the metallic inner vessel expanded with heat and at the same time air or a gas having a low thermal conductivity in the space expanded, which generated a pressure to push up the bottom wall of the inner vessel. When this pressure reached a certain level, the bottom wall having a concave surface was abruptly pushed up making an explosive sound and often deformed to have a convex surface, which resulted in hopping, scattering or deforming of the contents, when foods and drinks were contained in the vessel.

SUMMARY OF THE INVENTION

[0011] Therefore, in view of the abovementioned inconveniences and problems associated with the conventional vessels, an object of the present invention is to provide a handheld portable thermally insulated metallic vessel, which prevents an abrupt deformation with a sound upon expansion of the inner vessel or the thermally insulating medium, and can stably and effectively support the contents thereof.

[0012] The present invention is characterized in that in a handheld portable thermally insulated metallic vessel comprising a thermally insulated metallic vessel base and a lid to cover the vessel base, said vessel base being made by joining an outer vessel and an inner vessel in an integral fashion to have a airtight space between the inner vessel and the outer vessel and said airtight space being filled with a gas, and the bottom wall of the inner vessel is formed to have a planar surface. It is preferable that the side wall of said inner vessel is formed virtually perpendicular to said bottom wall. It is also preferable that said vessel base is a shallow container in which the width of said bottom wall is greater than the height of said side wall. It is further preferable that said handheld thermally insulated metallic vessel base consists of either a cylindrical peripheral wall with the bottom or a rectangular peripheral wall with the bottom. A desirable gas to be used is air or any gas having a thermal conductivity smaller than that of air.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a perspective view of the handheld portable metallic pan-type thermally insulated vessel of one embodiment example of the present invention.

[0014]FIG. 2 is a cross sectional view of the long side of the vessel in FIG. 1.

[0015]FIG. 3 is a cross sectional view of the short side of the vessel in FIG. 1.

[0016]FIG. 4 is a cross sectional view of the long side of the handheld portable metallic pan-type thermally insulated vessel of Comparative Example 1.

[0017]FIG. 5 is a cross sectional view of the short side of the vessel in FIG. 4.

[0018]FIG. 6 is a cross sectional view of the long side of the handheld portable metallic pan-type thermally insulated vessel of Comparative Example 2.

[0019]FIG. 7 is a cross sectional view of the short side of the vessel in FIG. 6.

[0020]FIG. 8 is a graph showing a comparison of the extent of displacement as a function of temperature change in the inner vessels of Example 1, Comparative Example 1, and Comparative Example 2.

DESVRIPTION OF THE PREFERRED EMBODIMENT

[0021] One example of the embodiment of the present invention will be explained in more detail below referring to FIGS. 1, 2 and 3. A portable thermally insulated metallic vessel 1 shown in this embodiment example comprises a thermally insulated metallic vessel base 2 and a lid 3 to cover the vessel base 2. The vessel base 2 is made in an integrated form by joining the opening edges of the inner and outer vessels 4, 5 by means of welding or the like to create an airtight space 6 between the inner vessel 4 and outer vessel 5. The inner and outer vessels 4, 5 are made of metal. Suitable metals are generally stainless steel, aluminum alloy or the like.

[0022] A gas having a low thermal conductivity is filled into said airtight space 6 to create a thermal insulating layer. The process of filling and sealing the gas having a low thermal conductivity can be carried out by drawing a vacuum inside the space 6 via a venthole 7 formed in the approximate center of the bottom wall 5 a of the outer vessel 5, introducing the gas having a low thermal conductivity, then closing the venthole 7 by adhering a sealing plate 8 on the exterior surface of the bottom wall 5 a to make the space 6 airtight. This venthole 7 can also be formed on the inner vessel 4. A gas consisting of at least one of krypton, xenon, and argon can be used for said gas having a low thermal conductivity as an insulating medium. Also, air can be used. In that case, formation of the venthole 7 is not necessary.

[0023] Said thermally insulated metallic vessel base 2 can be made into a vessel having a rectangular peripheral wall with a bottom, the bottom walls 4 a, 5 a of the inner vessel 4 and the outer vessel 5 is formed to have a planar surface, and the side walls 4 b, 5 b of the inner vessel 4 and the outer vessel 5 are formed virtually perpendicular to said bottom walls. Carrying handles 9, 9 are installed on each side wall diametrically opposite one another at the ends of the long side wall 5 b of the outer vessel 5.

[0024] In this embodiment, said lid 3 is formed also in an integral fashion by joining inner and outer walls 3 a, 3 b forming an airtight space 3 c between the inner wall 3 a and the outer wall 3 b, and a gas having a low thermal conductivity is introduced and sealed into said airtight space to form a thermally insulated structure.

[0025] Said thermally insulated metallic vessel base 2 can be shaped into a variety of shapes, for example, a vessel having a circular peripheral wall with the bottom, a reversed truncated cone-shaped vessel in which the bottom area is larger than the opening area, or a vessel having a rectangular peripheral wall with the bottom. However, a vessel having a rectangular bottom is preferable considering volumetric efficiency for the placement area, and a vessel base having a rectangular peripheral wall with the bottom in which the area of the bottom and the area of the opening are virtually the same is more desirable.

[0026] Further, as for the handheld portable thermally insulated metallic vessel 1 which is formed to have the planar surface of the bottom walls 4 a, 5 a of the outer and inner vessels 4, 5, a shallow bottom vessel, generally called a pan, is most desirable, in which the thermally insulated metallic vessel base 2 is a vessel having a rectangular peripheral wall with the bottom and the height of the side wall is smaller than the width of the bottom wall.

[0027] In the abovementioned handheld portable thermally insulated metallic vessel 1, any abrupt change in the shape on the bottom wall 4 a of the inner vessel 4 or an associated sound or spilling of the contents from tilting will not occur due to an increased temperature when heated foods or drinks are placed inside the inner vessel 4 or said thermally insulated vessel 1 is placed in a heated environment.

EXAMPLE 1

[0028] The thermally insulated metallic vessel base 2 having a structure as shown in FIGS. 1, 2 and 3 was manufactured for practical use as follows.

[0029] 1) Inner vessel 4: Stainless steel SUS 304 (0.6 mm thick) was used to make the vessel in which the bottom wall was 326 mm wide and 276 mm deep, the side wall was 111 mm high, the joining corner of the bottom wall and the side wall was R30 mm, and the joining corner of the side walls is R45 mm.

[0030] 2) Outer vessel 5: Stainless steel SUS 304 (0.7 mm thick) was used to make the vessel in which the bottom wall was 342 mm wide and 293 mm deep, and the side wall was 124 mm high.

[0031] 3) Insulating medium: Krypton was used.

[0032] The inner vessel 4 and the outer vessel 5 were shaped into vessels each having a rectangular peripheral wall with the bottom in which the bottom walls 4 a, 5 a had a planar surface and the bottom area and the opening area were virtually the same by setting each draft of the side walls 4 b and 5 b as one degree. In order to prevent heat radiation, metal oxides on the oppositely facing surfaces of the inner and outer vessels were removed to increase their luster instead of using any heat radiation preventing materials such as aluminum foil.

[0033] After the inner vessel 4 and the outer vessel 5 were joined in an integral fashion by TIG-welding the respective mouth portions of the vessels, the space 6 between the two vessels was vacuumed through a venthole 7 using a vacuum pump and then filled with krypton gas as an insulating medium at room temperature to an approximate atmospheric pressure, and several drops of an instant adhesive such as Aron Alpha (trade name, a product of Toa Gosei Chemical Industry, Co., Ltd.) were applied near the venthole 7 to seal the space airtight with the sealing plate 8 to make the thermally insulated metallic vessel base 2.

COMPARATIVE EXAMPLE 1

[0034] As shown in FIGS. 4 and 5, the thermally insulated metallic vessel base 10 was manufactured in the same manner as described in Example 1 above using the same material and the same measurements, except for the shape of the bottom wall 11 a of the inner vessel 11. The bottom wall 11 a was made to have a concave surface with R1420.5 to create the deepest depression in the center.

COMPARATIVE EXAMPLE 2

[0035] As shown in FIGS. 6 and 7, the thermally insulated metallic vessel base 20 was manufactured in the same manner as described in Example 1 above using the same material and the same measurements, except for the shape of the bottom wall 21 a of the inner vessel 21. The bottom wall 21 a was made to have a concave surface with R1420.5 mm to create the deepest depression in the center. Three ribs 21 b were formed inside the bottom wall 21 in the long side direction. These ribs 21 b were 200 mm long, 10 mm wide, and 2 mm high, and the pitch between the ribs was 40 mm.

[0036] In order to examine changes in the shape of the bottom wall of the inner vessel made of stainless steel according to the present invention, the thermally insulated metallic vessel bases of Example 1, Comparative Example 1 and Comparative Example 2 were placed in a thermostatic room and the displacement of the bottom wall was measured by changing the temperature. Results are shown in FIG. 8. In FIG. 8, line A is for Example 1, line B is for Comparative Example 1, and line C is for Comparative Example 2. The position of the bottom wall at room temperature was measured first and the shift of the bottom wall at a specified temperature from that position was referred to as the extent of the displacement.

[0037] As clearly shown in FIG. 8, in the thermally insulated metallic vessel base of Example 1, the extent of displacement was virtually proportional to the change in temperature, and a drastic change in the shape of the bottom wall was not observed so that the sound associated with the change from the concave surface to the convex surface was not generated. In the thermally insulated metallic vessel base of Comparative Example 1, the displacement in the bottom wall was extremely small up to 100° C.(0.5 mm), which was excellent, but at 120° C. it drastically increased to 8.7 mm, which abruptly changed the convex surface of the bottom wall to a concave surface and an explosive sound was simultaneously generated. When the displaced bottom wall was cooled, about 2 minutes later the shape of the bottom wall returned to its original shape generating an explosive sound. In the thermally insulated metallic vessel base of Comparative Example 2, the bottom of the inner vessel did not show drastic displacement as the base of Example 1; namely, the concave surface remained as it was and no explosive sound was generated. However, the extent of displacement of the bottom wall was large as compared to that in Example 1. Moreover, there remains problems, for example, the number of manufacturing steps has increased because of the rib forming process, and the bottom portions of the ribs formed on the bottom surface of the inner vessel cannot be completely cleaned upon washing as stains still remain at the portions.

[0038] As explained above, according to the present invention, abrupt deformation of the bottom wall of the inner vessel with an explosive sound can be prevented since the bottom wall of the inner vessel of the thermally insulated metallic vessel base has a planar surface, even when the inner vessel or the insulating medium expands when hot stuff is placed inside the vessel, or the vessel is placed in an environment at an elevated temperature such as in a drying room. Moreover, the bottom wall always remains as a planar surface, such that the contents can be stably held in the vessel and not tip over. Further, hopping of the contents due to the deformation of the bottom wall can be prevented.

[0039] For volumetric efficiency in the occupying area, the shape of the abovementioned thermally insulated metallic vessel base is preferably a vessel having a rectangular peripheral wall with the bottom in which the side wall of the inner vessel is virtually perpendicular to the bottom wall and the shape of the bottom area and the shape of the opening are virtually the same. Furthermore, it is practically most desirable to apply this invention to a handheld portable pan-type thermally insulated metallic vessel in which the height of the side wall is smaller than the width of the bottom wall. 

What is claimed is:
 1. A handheld portable thermally insulated metallic vessel comprising a thermally insulated metallic vessel base and a lid to cover the vessel base, said vessel base being made by joining an outer vessel and an inner vessel in an integral fashion to form an airtight space between the inner vessel and the outer vessel, and said airtight space being filled with a gas, wherein the bottom wall of an inner vessel is formed to have a planar surface.
 2. A handheld portable thermally insulated metallic vessel according to claim 1, wherein the side wall of said inner vessel is formed virtually perpendicular to said bottom wall.
 3. A handheld portable thermally insulated metallic vessel according to claim 1, wherein said vessel base is a shallow container where the width of said bottom wall is greater than the height of said side wall.
 4. A handheld portable thermally insulated metallic vessel according to claim 2, wherein said vessel base is a shallow container where the width of said bottom wall is greater than the height of said side wall.
 5. A handheld portable thermally insulated metallic vessel according to claim 1, wherein said handheld thermally insulated metallic vessel base consists of an oval or circular peripheral wall with the bottom.
 6. A handheld portable thermally insulated metallic vessel according to claim 2, wherein said handheld thermally insulated metallic vessel base consists of an oval or circular peripheral wall with the bottom.
 7. A handheld portable thermally insulated metallic vessel according to claim 3, wherein said handheld thermally insulated metallic vessel base consists of an oval or circular peripheral wall with the bottom.
 8. A handheld portable thermally insulated metallic vessel according to claim 4, wherein said handheld thermally insulated metallic vessel base consists of an oval or circular peripheral wall with the bottom.
 9. A handheld portable thermally insulated metallic vessel according to claim 1, wherein said handheld thermally insulated metallic vessel base consists of a rectangular peripheral wall with the bottom.
 10. A handheld portable thermally insulated metallic vessel according to claim 2, wherein said handheld thermally insulated metallic vessel base consists of a rectangular peripheral wall with the bottom.
 11. A handheld portable thermally insulated metallic vessel according to claim 3, wherein said handheld thermally insulated metallic vessel base consists of a rectangular peripheral wall with the bottom.
 12. A handheld portable thermally insulated metallic vessel according to claim 4, wherein said handheld thermally insulated metallic vessel base consists of a rectangular peripheral wall with the bottom. 